Keith Cowing's Devon Island Journal - 16 July 2002: Sealing greenhouses on Earth - and Mars; 6 wheeled rovers


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NASA HMP-2002/SpaceRef



Tom Graham installs Lexan to the aft end of the greenhouse

Tom Graham cutting Lexan

Keltey at the controls of the Argo ATV

Stephen Braham wearing Xybernaut wearable computing gear

Alain Berinstain driving "Priscilla"

Alain Berinstain and Charles Cockell give "Priscilla" the Argo a water test. Photo: HMP-2002/Brian Crucian
Walking up to the greenhouse this morning, I felt energized by the sight of a nearly completed structure. Damn this thing looks good!

With the Lexan installed on the sides of the greenhouse, the next task was to get it installed on either end. As I mentioned earlier, the instructions that accompanied this greenhouse left much to be desired. We compounded things by making some modifications peculiar to our project.

One modification was cutting some of the large Lexan panels in California such that they'd fit inside a Twin Otter. This would require us to install the Lexan in a wholly different fashion than the instructions called for. In essence, we had to assemble a patchwork of pieces and adapt the pieces we were provided.

Each piece of Lexan was hand-crafted. After I cut a piece of Lexan using a circular saw, we had to adjust the piece so as to make certain it would make a snug fit with what was already in place - and with the closed foam insulation that served to seal the seams between edges and other parts of the structure. While we would later caulk all cracks and seams, we still labored to get the pieces to be the best fit possible to as to reduce the amount of caulking that would later be done.

We took great care as we installed these Lexan panels to make sure that they were snug and that there were no air spaces to let heat out - or let blowing winter weather in. Even the smallest hole can allow a large amount of blowing snow (spindrifts) in when propelled by relentless winter winds.

We also had to worry about snow getting underneath the greenhouse. The alleviate this concern we had started to collect rocks to use as a foundation and windscreen. Not only would they serve to help anchor the greenhouse they'd also cut down on the amount of air that could pass underneath the greenhouse.

Combined with sheets of plywood along the base of the greenhouse, we were hoping that the snow under the greenhouse would be kept to a minimum when we arrived back here next year.

Once the Lexan is installed, and some other internal work is done, we'll add a dozen aircraft cables anchors that will attach the greenhouse structure to concrete reinforcement bars suck a meter into the permafrost. Between the several tons of weight provided by the greenhouse and another ton of hold down strength from these permafrost anchors, we expect that the structure will be solidly anchored against the worst that Devon Island has to offer.

The greenhouse we have assembled started as an off the shelf structure sold with support beams spaced 6 feet apart. I reduced this spacing to 4 feet so as to decrease the amount of unsupported Lexan surface area and increase the overall strength of the structure.

The heavily fortified greenhouse we are building is probably not what you'd want to build on the surface of Mars. Given the weak nature of the winds, you don't have to worry as much about building a structure to resist them - rather, you need one that can maintain a higher pressure inside than outside.

Rather, its is the constant polishing of the surface of materials that may come to be of concern. You need a material that will let in the wavelength range of light you want and block those you don't. You also want it to retain heat. The constant onslaught of Martian dust could, over time, affect the outer covering of any greenhouse material. As such, care will have to be given to the performance of greenhouse materials after years of abrasion by Martian dust.

Also of concern is the covering of the greenhouse by dust - thus blocking light. As such, a shape will have to be utilized that minimizes the chance of accumulating Martian dust. Providing astronauts with big brooms to clean the dust off might also be prudent.

One other thing that must be taken into account during Mars surface mission design is how much dust can be expected to be deposited on solar panels and how it will be blown off over time. Dust accumulation can have a direct effect upon the amount of power an unmanned rover or lander can expect to generate. This, of course, is less of an issue if the spacecraft has a nuclear power source although its ability to shed heat might be affected if too much dust piled up on its radiators.

Quicktime panorama: Base Camp 21 July 2002. 180 degree pan. Taken atop a rise next to a gully east of Base Camp. R-L Greenhouse, Base Camp, Maynard Hill. [Download]

[Get Quicktime]

Most scenarios for human missions include a nuclear reactor. As such, dust deposition on solar panels won't be as much of a safety issue. However, a series of photovoltaic panels are likely to be used for smaller gear and for back-up systems. See "Earth on Mars: Greenhouses on the Red Planet" for more thoughts on what it would take to build a greenhouse on Mars.

During the middle of the day we got another Twin Otter flight in from Resolute. Aboard was a small unmanned aircraft (UAV) that NASA was going to be testing in the coming days. Also aboard was the CSA's Argo ATV. This vehicle was much larger than the ATVs we had been using . In addition, it had 6 wheels, was much more maneuverable, and certifiably aquatic than a standard ATV.

There had been delays in getting the Argo over to the island. It was partially disassembled so as to get it to fit into a Twin Otter. In the process, Alain Berinstain, Keegan Boyd, Tom Graham and Jaret Matthews (who also had a smaller 6 wheeled ATV in camp) became experts in how to put one of these things together.

After parking the Argo in camp, the dogs had to inspect it. With very little coaching Keltey jumped aboard. Before we knew it she was posing with a paw upon the controls.

Eventually, the Argo was given a new name: "Priscilla" after one of the characters in the film "The Adventures of Priscilla, Queen of the Desert". Priscilla's striking blue color really made her stand out against the dull rocky arctic desert terrain.


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